Tremendous strides have been made to reduce the size of classic laboratory scientific analyzers. For some types of analyzers, e.g. Raman and infrared (IR) spectrometers, this has progressed to handheld, self powered instruments. These portable instruments now enable field use applications that were simply not possible in the past. Whereas handheld Raman spectrometers currently exist using standard silicon based detector arrays for visible and near IR sensing, some applications require even longer wavelength detector arrays, such as Indium Gallium Arsenide (InGaAs). These types of detector arrays are very expensive and require significant power for cooling. One prior art solution is to use a segmented optical modulator that has the ability to turn on or off selected wavelengths that are all directed to a single detector. The single detector is less expensive and requires little cooling power. Prior art has shown that spectrometers of this type can be implemented with optical light modulators based on micromirror arrays.
FIG. 1 illustrates a portable Raman spectrometer of the prior art. A laser source is filtered and then focused onto a sample. Inelastically scattered light from the sample is collected (eg. Stokes scattered light), passed through a filter that allows only wavelengths beyond that of the laser, and then directed to the entrance slit of a spectrometer. The spectrometer typically has an optical collimator (either a mirror or a lens) followed by a dispersive element (a grating or prism) where the incoming light is dispersed at different angles depending on the wavelength. The diverging but still collimated wavelengths are then focused (either by a lens or a mirror) on to a detector array e.g. a charge-coupled detector (CCD) array. Detector arrays are cost-effective in the visible range, up to 1.1 microns. In the near-IR range, the detectors are comparatively expensive.
FIG. 2 illustrates another prior art Raman spectrometer. The embodiment is similar to that shown in FIG. 1. In lieu of a detector array, a single detector is used. The dispersive element is tilted during the measurement to focus the wavelength of interest onto the single detector.
FIG. 3 illustrates another prior art Raman spectrometer. The embodiment is similar to that shown in FIG. 1. In lieu of a detector array, an array of micro-mirrors is used. Each micro-mirror in turn, reflects the wavelength of interest onto a single detector. The micro-mirror either reflects the light to or away from the detector. One wavelength or various combinations of wavelengths may be measured at a time.